1. Field of the Invention
The invention relates to a process for degreasing metal surfaces, especially aluminum and aluminum alloy metal surfaces. Aqueous compositions and methods of the invention provide satisfactory degreasing of metal surfaces for use in the aerospace industry. The compositions and methods of the present invention can be utilized to replace vapor degreasing operations in many metal fabricating operations.
2. Statement of Related Art
Many mechanical operations such as stamping, cutting, welding, grinding, drawing, machining, and polishing are used in the metal working industry to provide shaped metal articles. In metal working operations, lubricants, antibinding agents, machining coolants and the like are normally utilized to prevent binding and sticking of the tools to the metal articles in the various metal working operations. The lubricants, coolants, and antibinding agents and the additives present in these compositions usually leave an oily, greasy, and/or waxy residue on the surface of the metal which has been worked. The residue normally should be removed before the worked articles are given a protective surface finish or incorporated into a finished assembly.
Until the present time, it has been customary to clean oily, greasy, and/or waxy residues from metal articles by a vapor degreasing process. In a vapor degreasing process, the metal articles, at a temperature below the condensing temperature of a solvent for the oily, greasy and/or waxy residues, are suspended in vapors of refluxing solvent. The refluxing solvent condenses on the surface of the metal article, and the liquid solvent dissolves the oily, greasy, and/or waxy residues on the surface of the metal article. The condensing solvent with the high dissolving power for the contaminants to be removed from the surface of the metal article condenses on the surface of the article, dissolves the contaminants, and is returned to the source of the solvent vapor.
Solvents such as methyl ethyl ketone, methylene chloride, 1,1,1-trichloroethane, trichloroethylene, perchloroethylene, and the like are normally used in the vapor degreasing process. Since the oily, greasy, and/or waxy soils removed from the metal articles generally have a boiling point substantially higher than the boiling point of the refluxing solvent, the metal articles are contacted with a condensed solvent containing only relatively small quantities of the contaminants to be dissolved and removed from the metal articles.
Vapor degreasing is technically effective but economically and environmentally disadvantageous. The solvents are expensive, can be environmental pollutants, and require costly methods for reclamation and disposal. Special apparatus and processes are required to reclaim used solvent for reuse and to prevent solvent vapors from escaping from the vapor degreasing process. The solvent vapors are often hazardous to human health and some of them are suspected of promoting degradation of the earth's ozone layer. In view of the drawbacks in the use of the vapor degreasing process, many attempts have been made to replace vapor degreasing with aqueous based cleaning compositions. However, to date the aqueous cleaning methods have not been entirely satisfactory, particularly in preparing metallic surfaces of relatively low density, such as those of aluminum and aluminum alloys, for use in the aerospace industry, where the requirements for cleaning are particularly stringent.